Polyacrylamide gels containing DNA are used to separate and visualize acidic DNase activities derived from peripheral leukocyte subpopulations. Electrophoretic conditions are such that no destruction of substrate occurs during migration. After electrophoresis, incubation and staining reveals the presence of DNases. Cell populations from normal human donors, which are highly enriched for lymphocytes exhibit enzyme activity profiles different from these obtained from populations highly enriched for polymorphonuclear neutrophils. These profiles show only slight variation among donors. Sharp pH optima, which vary with the identity of the incubation buffer, are exhibited. Proper ionic strength is critical in the development of activity during incubation. Satisfactory visualization of activities is obtained using only 10 to the 6th power cells/gel. Cell populations from human donors with leukemia often exhibit activity spectra different from normal donor spectra. These variant spectra appear to be characteristic of particular types of leukemia. Visualization of positively charged DNases is obtained by electrophoresis in one dimension lacking polynucleotide, followed by migration in a second dimension containing DNA. Mobility in the second dimension is made possible by the presence of polycations. The two-dimensional activity patterns appear to correlate with the course of treatment administered to individual patients.